Hi, The way it works is pretty straightforward (from the surface.) * The radio signals whether the air is free or busy; * The QCU handles the frame queuing; * The DCU handles arbitrating between different TX queues, based on whether the NIC is currently RXing or whether the air is busy; * There's a bunch of timers in each DCU to implement contention/backoff (see AR_D_* registers in the FreeBSD/madwifi HAL, I don't know what they're called for ath5k.) * The DCU then gates the QCU and kicks off DMA. So the hardware is what decides when to trigger the TX DMA. In fact, for later NICs, they may start DMAing the frame _just before_ the IFS/backoff counters reach 0, just in case it wins the opportunity to talk over the air. You just setup everything to allow the NIC to begin TX DMA when it's ready to send things. :-) HTH, Adrian On 14 February 2012 12:06, Yiannis Yiakoumis <gyiakoumis@xxxxxxxxx> wrote: > Hi, > > I am reading the code and trying to understand what forces the packet > out of the card, or to be more clear, what runs CSMA/CA and when > detects a tx opportunity pushes the packet down to the phy. I can > track the packet all the way until it gets to start_tx_dma(), but I am > not clear what is the actual call that sends it out, and how this > relates with QCU (I am on a 5212). I suspect that it's within the > tasklet_schedule but wasn't able to find the details. > Also, does QCU get involved on a packet-per-packet basis, or does it > just set the initial values to the device's registers? > > Any help is much appreciated.. > > Thanks, > -- > Yiannis . > -- > To unsubscribe from this list: send the line "unsubscribe linux-wireless" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
